1. Field of the Invention
The present invention relates to electronically finding, locating, and mapping buried urban utilities electronically from the immediate surface above, and more particularly to blending of ground penetrating radar and electromagnetic gradiometer images and surface position fixes and then incrementally improving the displayable results with multiple passes.
2. Description of the Problems to be Solved
Finding stray, broken, lost, forgotten, misplaced, prohibited, or unlawful segments of pipes, utilities, and wires buried in the soil can be important for any number of construction, maintenance, security, defensive, economic, and operational reasons. Old maps, diagrams, notes, memories, and visual spotting are unreliable and fatiguing. Conventional electronic methods have not been performing as well as needed.
Electro-magnetic fields can both be induced into and sensed from wires and pipes from above on the ground surface of an area. Re-radiated magnetic fields can provide telltales of the locations and orientations of metallic and other electrically conductive objects, especially long metal pipes and wires.
Long-wavelength, gradiometric ground-penetrating radar (gGPR) methods can do better at mapping than conventional ground-penetrating radars (GPR) which use short-wavelength radar techniques like those developed during WW-II by the MIT Radiation Laboratory. The construction industry, in particular, has suffered a high rate of failures in the use of modern commercial versions of such short-wavelength GPR. A recent example of such a technology failure was demonstrated at Los Angeles airport during a reconstruction project when ground drilling ruptured a high-pressure gas line and the resulting leaking flammable gas exploded. A second misadventure hit an underground utility power supply to Terminal-I knocking out all power, and a third misadventure cut a large sewage line and flooded the nearby TSA headquarters with black water.
Gradiometric ground penetrating radar (gGPR) instrumentation and signal processing functionality takes the spatial or time domain derivative of phase-coherent illuminating and scattered/reflection radar signals. In the near field, Taylor's theorem derivatives of these signals determine distance to scattering/reflecting objects buried below a spatial cluttering geologic reflecting (SCGR) interface. The derivative of far field illuminating and reflecting interface plane wavefront is zero, making for high gain and high signal-to-noise-ratio detection.
Signal gradients can be very pronounced and change rapidly as electromagnetic gradiometer detection equipment is moved over areas with buried pipes and wires. These conductive objects will naturally re-radiate secondary electro-magnetic emissions. In contrast, far-field primary emissions from distant sources are characterized by near-zero difference signal gradients in the local area. Near-fields are dominated by dipole-type electric or magnetic fields. The sensing equipment has only to distinguish between the electric primary and magnetic secondary signal types to recognize nearby targets.
At least two basic kinds of gradiometer instruments have been used to measure magnetic field gradients. An axial gradiometer type places two magnetometers head-to-head on the same axis and wires them in series so they automatically cancel the common mode signals. Such measure the difference in the magnetic flux at a point. A planar gradiometer type spaces two magnetometers in parallel apart from one another to subtract one from the other at the receiver. The difference is the differential magnetic flux between the two magnetometers. For example, refer to our U.S. Pat. No. 7,675,289, issued Mar. 9, 2010. The axial and planar types will respond differently to spatial signals. The magnetic field component directions relative to the device's spatial orientation can be measured with vector magnetometers.
A single magnetometer can be used to collect readings point-by-point over a survey area. Each reading at each point is stored in a table and then the apparent magnetic gradients can be computed and displayed on a map. A three-axis magnetometer in a single pod can provide x,y,z magnetic axes measurements for even more complex calculations and information extraction.
Gradiometer instrumentation can sometimes be challenging to accommodate because of its size. Even full-size ground, air, and water vehicles can be pressed to provide enough room. The size, weight, and power (SWAP) requirements of new kinds of onboard sensors and devices can sometimes be too much for first generation systems. This is especially true of small remote-controlled vehicles, robots, and drones that are not fully integrated. In contrast, stand-alone sensors developed as individual mix-and-match add-ons waste too much in resources, and the combinations are difficult to house in tight accommodations.
Stolar Research Corporation (Rio Rancho, N. Mex.) has developed a broad line of vertical magnetic gradiometers (VMG) that can be used singularly, in pairs, and in arrays to sweep over roadways and open fields. Stolar VMG's can be carried by personnel on foot, vehicles, airplanes, kites, robots, and even as EMG sondes on drones. These products all descended from Stolar's earlier work with EM gradiometers on measuring coal deposits in underground mines.
New advances here in the remote sensing sciences combine multi-purpose, collocated sensors that also share system resources.
The American Public Works Association (APWA) has been promulgating its Uniform Color Code for Marking Underground Facilities Underground facilities. They want everyone to use colors of spray paint to mark on the ground surface the locations of buried utilities in accordance with a following designated color code.
WhitePre-marking of the outer limits of theproposed excavation or marking thecenterline and width of proposed linealinstallations of buried facilities.PinkTemporary Survey Markings.RedElectric power lines, cables or conduit,and lighting cables.YellowGas, oil, steam, petroleum, or otherhazardous liquid or gaseous materials.Orange Communications, cable TV, alarm or signallines, cables or conduits.BluePotable Water, irrigation, and slurrylines.PurpleSlurry and reclaimed.GreenSewers, drainage facilities or other drainlines.
The APWA guidelines for uniform temporary marking of underground facilities provides for universal use and understanding of the temporary marking of subsurface facilities to prevent accidents and damage or service interruption by contractors, excavators, utility companies, municipalities or any others working on or near underground facilities. Their One-Call damage prevention system is often required by Law to be contacted prior to excavation. White marks are painted or chalked to show the location, route or boundary of proposed excavation. Surface marks on roadways do not exceed 1.5″ by 18″ (40 mm by 450 mm). The facility color and facility owner identity may be added to white flags or stakes. Color-coded surface marks are used to indicate the location or route of active and out-of-service buried lines. Color-coded vertical markers (stakes or flags) are used to increase visibility and supplement surface marks. Marks and markers indicate the name, initials or logo of the company that owns or operates the line, and width of the facility if it is greater than 2″ (50 mm). Marks placed by other than line owner/operator or their agents are used to identify the designating firm. Multiple lines in a joint trench are marked in tandem. If the surface over the buried line is to be removed, supplementary offset markings are used. Offset markings are on a uniform alignment and meant clearly indicate the actual facility is a specific distance away.
Any excavation within the tolerance zone must be done with non-powered hand tools and other non-invasive methods until the marked facility is exposed. The width of the tolerance zone may be specified by Law. If not, a tolerance zone including the width of the facility plus 18″ (450 mm) measured horizontally from each side of the facility is recommended. The American Public Works Association encourages public agencies, utilities, contractors, other associations, manufacturers and all others involved in excavation to adopt the APWA Uniform Color Code, using ANSI standard 2535.1 Safety Colors for temporary marking and facility identification.
However, marking all the buried utilities in a whole city or even an airport is not very practical using the APWA methods. The conventional utility locating tools commonly used are only useful in small areas when lots of time is available.